Bread produced from wheat flour is a major component of the human diet in many areas of the world, providing most of the required calories and proteins in the diet. In lesser developed countries, the caloric contribution of bread to the diet may be as high as 80-90%. As much as 64% of the daily protein intake in the developing countries is derived from cereal grains from which bread is made. Flat breads, which are made of cereal grains, are the most ancient of breads, and remain especially popular in the Middle East and Indian subcontinents. Many types of flat fermented breads, such as Egyptian baladi bread, are to be found around the world. Standard characteristics include the flat shape, usually with an open, pocketed interior. The doughs are comprised of low protein flour of high extraction, water, salt and leavening agent, either yeast or lactic acid-producing bacteria as a sour starter. The formula for Baladi bread dough consists of high extraction (82 to 88%) flour, water salt, and 12 to 17% starter (fermented dough). Fermentation in the dough is initiated by the activity of wild bacteria and yeast which are present in the starter. For most flat breads the fermentation period is quite short, and is initiated by the activity of bacteria and yeast. The heart of the baking process for all flat breads is the naturally occurring sourdough starter containing microbes. The sourdough starter is responsible for the improved leavening action, the bread's sour taste and an extended shelf life.
Following the brief fermentation, the dough of most flat breads is divided, flattened to a form resembling a pancake on a wooden board dusted with wheat bran, and then proofed for another short period. The flattened dough is then baked at high temperatures (400.degree.-500.degree. C.) for a short time (1-3 min.). The flat piece of dough rises in the oven. Steam formation, rather than gas production, causes it to separate into two thin layers and form the characteristic pocket.
The formula and baking process for producing baladi, and other flat breads are as much a part of tradition as the bread itself. Accordingly, one of the objects of the invention is to provide the means whereby the product can continue to be manufactured economically, in a manner congruent with tradition, and also in such a way as to improve the nutritive value of flat bread. Although the conventional procedure described above yields an excellent product, it is subject to certain nutritional disadvantages as outlined herein and a primary objective of the invention is to provide a procedure which alleviates these disadvantages.
Normal cereal grains, including the wheat from which most breads are produced, are low in some of the essential amino acids, i.e., lysine, threonine, methionine, tryptophan and isoleucine, the so-called "limiting" amino acids. Such cereal grains can be considered low quality protein sources. Thus, cereal grain-based diets, prevalent in many areas of the world, may be deficient in some essential amino acids.
Research has proven that if humans lived primarily on cereal grains with no intake of animal protein, as is the case for people who have flat bread based diets, the protein received would be adequate if it were of a quality comparable to animal protein. Thus, improving the nutritive value of fermented breads such as flat-breads, is of considerable importance to lesser developed countries and other wheat importing nations. This is most effectively accomplished by increasing the lysine content of cereal protein. Further efforts may involve increasing the threonine content thereof, as threonine is generally the next most limiting amino acid after lysine. Accordingly, it would be of tremendous importance and benefit to produce a bread or wheat product with an increased content of the limiting amino acids, thus raising the nutritional value of such products.
The nutritive value of the bread depends upon the protein level in the flour and on the balance of various amino acids that make up the protein. Normal cereal grains, including wheat, are low in some of the essential amino acids; that is, lysine, threonine, methionine, tryptophan, and isoleucine, the so-called limiting amino acids. This limitation causes protein in the bread to be poorly utilized by the body. Accordingly, it would be of tremendous importance and benefit to produce a wheat bread with an increased content of limiting amino acids, thus raising the nutritional value of such products. In order for the human body to properly utilize protein, the essential amino acids must be available simultaneously and in the most advantageous proportions. The FAO (Food and Agriculture Organization) recommends a minimum lysine ratio of 5.2% in protein as an ideal proportion of lysine for infants. Wheat protein generally has only about 50% of this ideal recommended level. If lysine can be added to such wheat-based diets, a higher value of wheat protein can be realized.
Such approaches as breeding and growing cereal grains for quality have shown that increasing the nutritional value of cereal grains leads to a decreased yield and vice versa. Blending wheat flour with alternate protein sources such as soybean meal or fish meal has been generally unacceptable because of the cost of the protein source and taste preference or consumers' acceptance.
The prior art teaches that various microorganisms and their mutant strains have been used to produce lysine. For example, U.S. Pat. No. 2,841,532 to Kita et al discloses the use of E. coli to produce lysine. U.S. Pat. No. 2,979,439 to Kinoshita et al teaches that lysine may be produced from a mutant of Micrococcus glutamicus. U.S. Pat. No. 3,524,797 to Boyd et al discloses a method wherein lysine is produced by cultivating a double mutant of Micrococcus glutamicus. In U.S. Pat. No. 3,527,672 to Kubota et al, lysine is produced from mutant strains of Brevibacterium lactofermentum. U.S. Pat. No. 3,756,916 to Leavitt teaches specific methods for isolating a mutant strain of an amino acid-producing microorganism, usually Brevibacterium glutamicus. U.S. Pat. No. 3,905,866 to Watanabe et al describes a process for the production of lysine by a mutant strain of Pseudomonas or Achromobacter. U.S. Pat. Nos. 4,275,157 to Tosaka et al and 4,411,997 to Schimazki et al teach the production of lysine by culturing mutants of Corynebacterium or Brevibacterium.
None of these prior art teachings, however, teach or suggest the inoculation of lysine-excreting mutant strains into a bread or wheat product to enhance the lysine content thereof and thereby increase the nutritional value.
The prior art also discloses that it is known to use bacteria in the production of bread. For example, U.S. Pat. Nos. 3,734,743 and 3,891,773 to Kline et al teach the use of Lactobacillus sanfrancisco in preparing sourdough breads. U.S. Pat. No. 3,963,835 to Gryczka teaches that wild type Lactobacillus fermenti may be used to produce sourdough bread. However, to Applicants knowledge, there has not been any disclosure for improving the nutritive value of fermented breads through the use of lysine-excreting microorganisms or use of lysine-excreting bacteria in a bread or wheat products.